Coding of physiological signals



Aug. 10, 1965 N. A. ROTH 3,199,508

CODING OF PHYSIOLOGICAL SIGNALS Filed April 25, 1962 2 Sheets-Sheet lAm. VOLTAGE FRE UENCY TR 8 SS ELECTRODES ELECTRODE AMPLIFIER DIVIDERGENEgATOR 8 LINE SELECTOR AND SWITCHES MODULATOR (FIG.4)

T f T f i SBT i1 SljT (-28 +V k-fis I R? R8 76 R2 R3 I gm R5 R6 D2 m3%RH :02 Rl2 Rl4 COMMON 62 I INVENTOR Fi 4 NORMA/V ROTH Aug. 10, 1965 N.A. ROTH CODING OF PHYSIOLOGICAL SIGNALS 2 Sheets-Sheet 2 Filed April 25,1962 INVENTOR NEH United States Patent This invention is limited to thefield of electronicmedical instrumentation and more particularly toelectronic apparatus for use with medical instrumentation which sensesphysiological diagnostic waveforms emanating from .a human body, such asan electrocardiogram (ECG), an electroencephalogram (EEG) and the like.

A recent trend in the medical profession is toward a system ofcentralized processing of physiological data, such as ECG and EEGwaveforms, for analysis and diagnosis. in this .ty e of system, thereadings taken by a physician or tnaincd nurse at the doctors office,clinic or hospital are transmitted to a remote central location. Thelocation is staffed by highly skilled specialists and is equipped withelectronic devices for ensuring rap-id and accurate diagnosis. A systemof this type provides an en cient, high-grade service to a large segmentof the medical field.

There are various ways of implementing this type of system. Among thesystems in operation today is one in which amplified reproductions of 16ECG or EEG waves, as they are detected on the patient, are transmittedin real-time, for example via telephone lines, from a hospital ordoctors office to the remote central processing location. At the centrallocation the waveforms are visually displayed to be viewed by a medicalspecialist who makes his diagnosis and transmits his opinion back to thecalling hospital or doctor.

Another system contemplates the use of electronic data processingdevices such as digital and analog computers to perform the diagnosis.As in the previously mentioned system, the waveforms are transmitted inreal-time mode to the central data processing area where they areinputted to the electronic equipment. In general, the signal waveformsare inserted into a computer via peripheral equipment such as a magnetictape.

in both of the above systems it is often possible that an immediatediagnosis is not required so that the ECG or EEG readings can be storedin a magnetic tape which is later delivered to the central location forprocessing. Additionally, it is usually necessary to retain the readingsin a storage device such as a magnetic tape in order to maintain themedical history of the patient for possible future use in diagnosis. Itis a general object of this invention to provide apparatus for use in acentralized medical data processing system.

It is a more specific object of this invention to provide apparatus foruse in transmitting identified physiological diagnostic wave signals,such as ECG and EEG signals, from their source to a remote centralprocessing location.

A further object of this invention is to provide apparatus for use in .asystem for magnetic-ally recording signal representations ofphysiological diagnostic waves such as ECG, EEG and the like.

Still a further object of this invention is to provide apparatus forfurnishing selective identification coding along with the transmitted orrecorded physiological diagnostic Wave signals.

3,199,5(98 Patented Aug. 10, 1965 Yet another object of this inventionis to provide the immediately preceding object wherein the codingapparatus is relatively simple to operate and maintain.

Still another object of this invention is to provide semi automaticidentification of recorded physiological signals.

In the embodiment of this invention described herein, the physiologicwaveforms detected by electrodes coupled to the body are transmitted toan amplifier having high fidelity characteristics. The amplifier outputis coupled via a coding section into a combined carrier-Wave frequencygenerator and modulator circuit, the output of which is coupled to atelephone line for transmission to a remote location. The coding sectionincludes means for electively switching the modulator input to theamplifier output or one of a plurality of respectively different DC.voltage levels. In this manner codes identifying the patient, thedoctor, the calling source, etc, are transmitted along with thephysiological signals for record-keeping purposes and for associatingthese signals to the respective patients.

These and other objects and features will become apparent in the courseof the following detailed description, in which:

FIG. 1 is a block diagram of an embodiment of this invention;

PEG. 2 is a preferred embodiment of the selectively alterable codingcircuit which constitutes anothe aspect of this invention for use in theapparatus of FIG. 1;

FIG. 3 is an electrical schematic of an illustrative amplifier for usein the FIG. 1 embodiment;

FIG. 4 is an electrical schematic of an illustrative frequency generatorand modulator circuit for use in FIG. 1.

In the block diagram of BIG. 1, ECG electrodes, shown generally as 19,are coupled in the well-known manner to the various parts of the body,usually the legs, arms and chest. The low-level, low-frequencydiagnostic Waves, usually in the order of less than one millivolt andranging from about one to fifty cycles per second, are coupled throughan electrode selector switch 12, which is wellknown in the art, to theinput of amplifier M via line 16. The amplifier has characteristics ofhigh gain with a very accurate reproduction of the input signal toretain the critical portions of the diagnostic waves while providingsuificient power to drive a utilization device such as a strip recorder,magnetic tape, or a frequency modulating circuit, as will subsequentlybe described. The amplifier output signal is coupled via output line 18to the input of coding section Zii.

As will be subsequently described in greater detail in reference to FIG.2, the coding section Zii preferably comprises an output signal line 22,a DC. voltage divider network and a plurality of manually operableswitches. The switches are connected in such a manner as to provide themeans for selectively setting the signal line 22 to the amplifier outputor to one of a plurality of different D.-C. voltage levels from thevoltage divider.

The frequency generator and modulator circuit (EC-M) includes a circuitfor producing a carrier wave signal and a circuit for modulating thecarrier in accordance with the signal appearing at the input thereto viasignal line 22. In a preferred embodiment, the carrier isfrequencymodulated although it is within contemplation of the instantinvention to use amplitude modulation. The A.-Ci signal representationsof the physiological waveforms outputted by the amplifier i3 and theD.-C. voltage levels provided by the coding section 21) can beconsidered to be electrical analog signals. The modulation of thecarrier wave effectively digitizes these signals with respect to areference level so that the relative magnitudes of the D.-C. and A.-C.signals can be represented. This will become more apparent from thesubsequent more detailed description of the FG-M.

The modulated output of the FG-M 24 is coupled to a transmission linevia line 26. The transmission line is preferably a telephone lineconnecting the calling testing location, such as a doctors office or ahospital, to the remote central processing location. It is contemplatedthat the teachings of this invention are readily adaptable for othertransmission systems such as wireless radio communication.

Referring now to FIG. 2 there is shown a preferred embodiment of thecoding section 20 of FIG. 1. The coding section, in combination with theother sections of the apparatus of FIG. 1, provides an importantcontribution to the utility of the instant invention since it providesthe means for supplying identification information in conjunction withthe physiological data so that the latter can be specifically related toan individual patient, time of day, the treating physician and otherimportant criteria. Also, the identification information allowsrecording and maintaining of medical history.

The output signal line 22 is connected in common to one terminal of tenmanually operable switches, shown in their open position, respectivelylabelled SL810. Since these terminals are electrically connectedtogether they are labelled collectively as 28. A signal input terminal31) receives the output of amplifier 14 and is coupled to the otherterminal, 32, of switch S1 through capacitor C. The capacitor providesD.-C. isolation between the amplifier output and the signal line 22 whenS1 is closed while presenting negligible impedance to the A.-C. signaloutput from the amplifier. Connected across a D.-C. voltage source V,which may be in the range of about 20 volts and as symbolically shown bybattery 34, is a voltage divider network comprising variable resistorsR1 and R2 and fixed resistors RS-Rltl in seriatim. At the junction ofevery two resistors in the voltage divider the other terminal of each ofthe switches 52-519 is connected. All of the switches Sl-Sltl have anumber designation, respectively -9, and all are mechanically linkedtogether, by means not shown, so that only one is operable at one time.In other words, if one of the switches is in the closed position, manualclosing of any of the other switches will cause the previously closedswitch to open. In general, the voltage divider resistors are selectedand adjusted so that as each of the switches, respectively 52-510, issuccessively closed the D.-C. potential in line 22 increases in equalincrements. Additionally, it is within contemplation of the inst-antinvention that the voltage divider network can be designed to placesignal line 22 at the same D.-C. potential when switch S is closed as itis when switch S1 is closed.

The operation of the coding section of FIG. 2 in the combination of FIG.1 can best be described by an illustrative example. As will besubsequently described in greater detail, the modulator portion ofcircuit 24 will effect a transmission line output signal of a differentfrequency for each respectively different D.-C. potential applied to itsinput via signal line 22. In the overall system each subscribing doctoror hospital is given a code designation. Assume, in this example, thecalling physician has a five digit code of 19247. After initial contactwith the central processing location has been established but prior tothe transmission of the ECG readings, the doctor manually closesswitches labeled S2, S16, S3, S5 and S8 in that order. The D.-C.potentials at terminals 35, 38, 40, 42, and 47 of said switches aresuccessively applied to signal line 22 to cause, through the modulatorcircuit, correspondingly different frequency signals on the outputtransmission line 26. At the receiving central processing location thesesignals are recognized as identifying the physician. In a similarmanner, each patient can be assigned different codes which are alsotransmitted for identification. Similarly, the ECG readings can beidentified in respect to each of the particular electrodes. After all ofidentification data has been transmitted switch S1 is closed to applythe amplifier output to the signal line 22 for transmission to theremote location through the FG-M circuit.

FIG. 3 is an illustrative electrical schematic of a relativelyhigh-gain, high-fidelity amplifier for use in the embodiment of thisinvention. The input terminal 46 is connected to signal line 22. Thefirst two stages include .a pair of NPN transistors, 48 and 59,connected in the emitter follower configuration to provide a high inputimpedance to the low-level A.-C. input signal. The remaining "fourstages are designed to provide the desired amplification Withoutintroducing distortion. Intermediate transistor 52 and the outputtransistor 54 there is a reject circuit which is designed to filter outthe undesirable effects caused by power line frequencies. Because of therelatively low signal levels and the importance of faith fullyreproducing the input signal at an amplified scale, it is essential thatinterfering noise be filtered. Since power line frequencies are so closeto the range of signal frequencies they are generally the mosttroublesome. The amplifier output is connected to line 18 via outputterminal 55. Typical orders of magnitude are a 750 millivolt outputsignal produced in response to a one millivolt input signal.

Referring now to FIG. 4, in general the portion of the circuit to theleft of broken line 58 can be considered as the modulator circuitrywhile the remaining portion can be considered as a frequency generator.For descriptive purposes the circuits are treated in a combined mannersince the signal output frequency developed by the frequency generatoris dependent on the signal inputted thereto from the modulator circuit.

Input terminal 64) is connected to the signal line 22 from the codingsection 20. D.-C. voltage source +V provides power for the circuit andthe D.-C. as well as A.-C. signal common line is labeled as such at 62.The base element of NPN transistor Q1, which is connected in the emitterfollower circuit configuration to present a high input impedance, isconnected to the input terminal 60. Resistor R10 and capacitor C2 form aseries RC integrator circuit with a capacitor being charged by theemitter current of transistor Q1. Unijunction transistor Q2 has itscontrol electrode 64 connected to the junction of resistor R111 andcapacitor C2 and its emitter-collector circuit, including resistors R3and R12 in series, is connected across the D.-C. voltage source +V. Theemitter current of transistor Q1 flowing through resistor R10 chargescapacitor C2 toward the potential applied to the base of transistor Q1.When the charge across C2 reaches the firing potential of theunijunction transistor Q2, it conducts heavily and a short RC timeconstant discharge path is provided through resistor R12. When thecharge across C2 falls below the threshold potential of Q2, the lattercuts off and C2 again starts charging. In this manner, a sawtoothwaveform signal is developed across C2 and is applied to the controlelectrode 64. Since R10 is in the order of one-hundred times the valueof R12, the rise time of the leading edge of the sawtooth wave isconsiderably greater than the fall time of the trailing edge. Thefrequency of the sawtooth wave varies in accordance with the magnitudeof the potential at input terminal 65). When the unijunction transistorQ2 conducts, the signal appearing across R12 is coupled to the base oftrigger transistor Q3 via line 66 to provide the modulating signal inputto the frequency generator.

The frequency generator is essentially a one-shot triggeredmultivibrator comprising a pair of NPN transistors, Q4 and Q5, having acommon emitter resistor, R14. The collector 68 of transistor Q4 iscoupled to the base 70 of transistor Q5 through capacitor C1. Thetriggering input pulse is applied to capacitor C1 through diode D1 whichis connected to collector 72 of transistor Q3. Battery 74, in theemitter circuit of Q3, is polarized to back bias the emitter-basejunction of NPN transistor Q3.

When the mutlivibrator transistor Q5 is conducting its collector and theoutput terminal 76 connected thereto are at a relatively low potentiallevel. A pulse signal from the modulator circuit applied to the base ofthe triggering transistor Q3 causes it to conduct to apply a negativepulse to base 70 of transistor Q5 from the collector of Q3 through diodeD1 and capacitor C1. This causes Q5 to cut off, driving the outputterminal 76 to a positive potential level. Feedback to transistor Q4through the common emitter resistor R14 causes Q4 to conduct whichfurther aids in keeping Q5 cut oil. When capacitor C1 becomes fullycharged, base 70 of Q5 rises to a level sulficient to cause Q5 toconduct. This in turn causes Q4! to cut oil so that the multivibratorcircuit is returned to its initial stable condition and the outputterminal returns to a relatively low potential level. Subsequent inputpulse signals via line 66 result in repeated operations as describedabove. Since the repetition rate of the output signal at terminal 76 isdetermined by the frequency of the pulse signals on line 66 and thelatter, in turn, varies with the potential of the input signal at inputterminal 69, it can be seen that the transmission line signal, which isobtained from terminal 76, is modulated in accordance with the datainput at terminal 66. As previously described the latter is selectivelyeither coded identification data in the form of D.-C. potentials oramplified physiological signals from the amplifier, the selection beingmade in the coding section.

Although in general the coding section is utilized in the combinationdescribed for providing identification of medical data transmitted to aremote location, the instant invention contemplates other utility. Forexample, in the event the diagnostic waveforms are recorded directlyonto a strip recorder so that the FG-M circuit is not required, theoutput of the coding section on signal line 22 is connected directly tothe strip recorder. This alleviates the burden normally encountered inidentifying the strip chart records since the manually operableselective switching of the coding section semi-automatically idenitfieseach record so that hand entries are not required. It is further withincontemplation of the instant invention that a recording device, such asa magnetic tape, can be coupled directly to the output terminal 76 torecord the diagnostic signals along with the identifying signals.

Although the foregoing detailed description was in reference toidentification and transmission of ECG signals, it is within the scopeof the instant invention to include other physiological signals, ECGsignals being only illustrative and not limited.

It is understood that suitable modifications may be made in thestructure as disclosed provided such modifications come within thespirit and scope of the appended claims. Having now, therefore fullyillustrated and described my invention, what I claim to be new anddesire to protect by Letters Patent is:

1. In combination: a plurality of electrical probes each adapted forsensing physiological signals of a different nature; an amplifier havingits input coupled to said probes for producing output signals which areamplified substantial reproductions of said sensed physiologicalsignals; a D.-C. voltage divider network for providing a plurality ofD.-C. electrical reference coding signals; a signal output line fortransmitting electrical signals to a utilization device; and means forselectively switchng said signal output line to the output of saidamplifier or respectively different ones of said voltage divider codingsignals whereby each of the respective physiological signals appearingon said signal output line is suitably identified by associated D.-C.electrical coding signals on said output line.

2. In combination: a plurality of electrical probes adapted for sensingphysiological signals; an amplifier coupled to said probes for producingoutput signals which are amplified substantial reproductions of saidsensed signals; a signal output line; a D.-C. voltage divider networkfor providing a plurality of respectively different D.-C. potentials; afirst manually operable switch coupling said amplifier to said signaloutput line for transferring the amplifier output signal to said outputline when in the electrically closed condition; and a plurality of othermanually operable switches connected between said voltage divider andsaid output line for transferring said respectively different potentialsthereto when in the electrically closed condition whereby each of thephysiological signals outputted by said amplifier to said output line isassociated with identifying D.-C. sgnals appearing on said output line.

3. The combination of claim 2 wherein only one of said switches can beclosed at any one time.

4. In combination: a plurality of electrical probes adapted for couplingto an animal body for sensing physiological signals emanating therefrom;an amplifying circuit having an input and an output, said amplifieroutputting amplified substantial reproductions of its input; means forselectively coupling each of said probes to the amplifier input; afrequency generator for producing a carrier wave signal; a modulatingcircuit coupled to said frequency generator for modulating said carrierwave in response to and in accordance with signals received at itsinput; a D.-C. voltage divider network for providing a plurality ofrespectively different D.-C. potentials; and switching means forselectively applying said amplifier output signals and said D.-C.potentials to the input of said modulating circuit whereby each of themodulating physiological signals on the carrier wave is identified bycorresponding D.-C. potentials which modulate the carrier wave.

5. The combination of claim 4 wherein said switching means comprises aplurality of manually operable switches.

6. The combination of claim 5 characterized by only one of said switchesbeing operable at any one time.

7. The combination of claim 6 wherein one of said switches is connectedbetween the amplifier output and said modulating circuit input and theothers of said switches are each connected between the respectivelydiffcrent potential points on the voltage divider network and themodulating circuit input.

8. In combination: a plurality of electrical probes adapted for couplingto an animal body for detecting physiological dignostic waves emanatingtherefrom; an amplifying circuit having an input and an output, saidamplifier outputting substantial reproductions of its input signals;means for selectively connecting each of said probes to the amplifierinput; a frequency generator for producing a carrier signal wave; amodulating circuit coupled to said frequency generator for modulatingsaid carrier wave in response to and in accordance with signals appliedto its input; a signal line connected to the input of the modulatingcircuit; a first manually operable switch for coupling the amplifieroutput signal to said signal line when in the electrically closedcondition; a D.-C. voltage divider network for providing a plurality ofrespectively different D.-C. potentials; and a plurality of additionalmanually operable switches each connected between a respectivelydifferent potential point in said network and said signal line forselectively setting the modulating circuit input to a corresponding oneof said D.-C. potentials when in the electrically closed condition formodulating the carrier signal with corresponding identification signalsfor each of the modulating amplifier output signals.

9. The combination of claim 8 characterized by only one of said switchesbeing operatively in the electrically closed condition at any one time.

References Cited in the file of this patent UNITED STATES PATENTS Brown324-115 Krochrnann 340-207 Wengel 340-201 Fizzell 123-21 Howe 340-201Miller 128-206 Marchand 128-206 X Gilford 128-205 Partridge 128-206Goolkasian 128-205 Roepke 122-205 Kagan 128-206 Richards 128-206Kompelien 128-205 Clynes 128-2.1

OTHER REFERENCES Sarbacher: Encyclopedic Dictionary of Electronics,published 1959 by Prentice-Hall.

l0 RICHARD A. GAUDET, Primary Examiner.

RICHARD J. HOFFMAN, LOUIS R. PRINCE,

Examiners.

1. IN COMBINATION: A PLURALITY OF ELECTRICAL PROBES EACH ADAPTED FOR SENSING PHYSIOLOGICAL SIGNALS OF A DIFFERENT NATURE; AN AMPLIFIER HAVING ITS INPUT COUPLED TO SAID PROBES FOR PRODUCING OUTPUT SIGNALS WHICH ARE AMPLIFIED SUBSTANTIAL REPRODUCTIONS OF SAID SENSED PHYSIOLOGICAL SIGNALS; A D.-C. VOLTAGE DIVIDER NETWORK FOR PROVIDING A PLURALITY OF D.-C. ELECTRICAL REFERENCE CODING SIGNALS; A SIGNAL OUTPUT LINE FOR TRANSMITTING ELECTRICAL SIGNALS TO A UTILIZATION DEVICE; AND MEANS FOR SELECTIVELY SWITCHING SAID SIGNAL OUTPUT LINE TO THE OUTPUT OF SAID AMPLIFIER OR RESPECTIVELY DIFFERENT ONES OF SAID VOLTAGE DIVIDER CODING SIGNALS WHEREBY EACH OF THE RESPECTIVE PHYSIOLOGICAL SIGNALS APPEARING ON SAID SIGNAL OUTPUT LINE IS SUITABLY IDENTIFIED BY ASSOCIATED D.-C. ELECTRICAL CODING SIGNALS ON SAID OUTPUT LINE. 